1. Field of the Invention
This invention relates generally to a method and apparatus for controlling an internal combustion engine and more particularly to a microprocessor-based electronic engine control system having a memory preprogrammed with various control laws and control schedules and being responsive to one or more sensed engine-operating parameters for generating signals for controlling engine functions such as fuel injection, ignition timing, EGR control, or the like.
2. Statement of the Prior Art
Many of the patents of the prior art recognize the need for employing the enhanced accuracy of digital control systems for more accurately controlling one or more functions of an internal combustion engine.
U.S. Pat. No. 3,969,614 which issued to David F. Moyer, et al on July 13, 1976 is typical of such systems as are U.S. Pat. No. 3,835,819 which issued to Robert L. Anderson, Jr. on Sept. 17, 1974; U.S. Pat. No. 3,904,856 which issued to Louis Monpetit on Sept. 9, 1975; and U.S. Pat. No. 3,906,207 which issued to Jean-Pierre Rivere, et al on Sept. 16, 1975. All of these Patents represent a break-away from the purely analog control systems of the past, but neither the accuracy, reliability, or number of functions controlled is sufficient to meet present day requirements.
Future internal combustion engines will require that emissions be tightly controlled due to ever-increasing governmental regulations, while fuel consumption is minimized and drivability improved over the entire operating range of the engine. None of the systems of the prior art provide a method and apparatus for controlling the operation of an internal combustion engine over even a substantial portion of its operating range with sufficient accuracy to minimize emissions and fuel consumption while simultaneously improving drivability.
The systems of the prior art have not normally attempted to use an oxygen sensor-based feedback system for control purposes due to the extreme difficulty in obtaining reliable data from existing oxygen sensors. Furthermore, the oxygen sensor signal processors of the prior art utilize dedicated electronic analog and digital integrators to implement particular control schemes destroying system flexibility while increasing cost and size considerations. Prior art attempts to use oxygen sensor systems with digital engine control systems have uncovered horrendous problems inherent in the sampling nature and processing speed requirements of current systems which still require that an integration of the oxygen sensor signal must be accomplished over one revolution external to the computer and none of the systems of the prior art have solved any of these problems to produce a reliable oxygen signals integrator for use with a microprocessor-based electronic engine control system.
The present invention avoids all of the problems of the prior art and employs an oxygen sensor feedback loop digital electronic signal integrator which can be used in conjunction with a microprocessor-based electronic engine control system for accurately determining air/fuel ratios existing in the exhaust systems of the engine and for performing precise engine control functions in response thereto to achieve a highly accurate and reliable closed-loop oxygen sensor-based digital control system for use with the engines of automobiles, other motor vehicles, and the like.